Conventional sensor units are connected via terminal units to evaluation apparatuses for evaluating the sensor signals. In conventional fashion, an interface for connecting the sensor unit to the evaluation unit is equipped with a large number of terminal units, in particular when a measuring resistor must be provided in order to evaluate one of the current signals furnished by the sensor unit.
A conventional circuit assemblage of this kind is shown in FIG. 2. The sensor unit, which can be embodied e.g. as a peripheral acceleration sensor (PAS), is connected via terminals 2 and 2′. Usually a sensor signal dependent on the measured effect is measured as a current signal, in the case depicted in FIG. 2 as a current IPAS. For evaluation of the current signal and for further amplification of the measured signal obtained from the current signal, the current signal must be converted into a voltage signal. This purpose is usually served by a measuring resistor MW that is connected in series with sensor unit PAS. As shown in FIG. 2, measuring resistor MW is disposed between terminal 2 and a terminal 1. A voltage UPAS dropping across measuring resistor MW is delivered to an amplifier unit V via separate lines. The voltage UPAS dropping across measuring resistor MW is ultimately measured in amplifier unit V and outputted to an output unit A as an output signal a. A current IPAS dependent on acceleration values that are obtainable using sensor unit PAS can therefore be measurable via a voltage drop UPAS of this kind.
Sensor PAS is also connected, via terminal 2′ and a terminal 1′, to a system ground M. Because the voltage drop also depends on the supply voltage U0 that is made available, which is made available between terminal 1 and terminal 1′, it is necessary that supply voltage U0 not be subject to any fluctuations. Conventional methods use a support capacitor C, connected between terminal 1 and ground M (see FIG. 2), to compensate for voltage fluctuations that may be produced by factors such as external interference. The supply voltage is usually obtained from a battery unit B. Inserted between battery unit B and terminal 1 is a mispolarity protection unit VS which ensures that inadvertent mispolarities of the supply voltage do not damage downstream electronic components or the sensor unit.
Be it noted that one skilled in the art knows how to design an amplifier unit V in order to amplify a voltage difference signal UPAS delivered to the amplifier unit, and how to make an output signal a available at output A of amplifier unit V, so that a detailed explanation of amplifier unit V is omitted here.
Measurement systems that use sensor units PAS must be designed in variable fashion so that sensor units PAS are exchangeable. Because of production tolerances, however, it is impossible to obtain sensor units PAS that generate exactly reproducible currents IPAS as a function of a measured signal (e.g. an acceleration signal). For this reason, in conventional circuit assemblages measuring resistor MW must likewise be exchanged or replaced in the event of an exchange or replacement of sensor device PAS. This results in considerable complexity in terms of circuit engineering, thereby disadvantageously increasing the cost of the entire circuit assemblage. It is critical In safety-relevant applications, moreover, if measuring resistor MW must be exchanged along with sensor unit PAS, since errors in allocating measuring resistor MW to sensor unit PAS can easily occur.
A further disadvantage with the conventional sensor evaluation apparatus is that both sensor unit PAS and measuring resistor MW must be exchanged, since at least three terminal pins—i.e. terminals 1, 2, and 2′ in FIG. 2—must be reconnected in this context. In a conventional measuring system, the control and evaluation apparatus thus creates a need for two terminal units to the electronic circuit assemblage, and a ground terminal for connection to ground M, at the interface between sensor unit PAS and the control and evaluation apparatus. The terminal pins (terminal units) for connection to the electronic circuit unit are labeled in FIG. 2 with the reference characters 1 and 2, while the ground connection terminal (terminal pin) is identified by the reference characters 1′ and 2′.
Because the conventional control and evaluation apparatus is operated with mispolarity protection unit VS using a non-stabilized battery voltage B, it is disadvantageously necessary to make available, at the output of the energy supply unit (which is made up of battery B and mispolarity protection device VS), a capacitor C that is connected between an energy supply terminal E and ground M. In conventional systems, a smoothed energy supply voltage U0 is generated in this fashion.